1. Field of the Invention
The present invention relates generally to shock absorbers and, more specifically, to a pneumatic spring system for bicycles that could be used to retrofit an existing coil suspension system or could be installed as an independent unit. Irregularities on a riding surface cause destructive vibrations that reverberate throughout the bicycle's structure and promote wear and tear on the bicycle while causing discomfort and contributing to cyclist injuries. The proliferation of mountain biking and BMX racing has necessitated incorporating shock dissipation systems to absorb the force incurred by the wheels impacting the ground. These shock dissipation systems are usually contained within the wheel fork members thus minimizing the force of impact that is retained by the bicycle frame, including the handlebars which are in direct contact with the rider. These shock absorbers include coil based spring systems, gas-impregnated rubber, leaf springs, and compressed air among others.
The present invention overcomes the shortcomings of the prior art by introducing an adjustable pneumatic spring shock absorber with a tunable position sensitive spring rate for bicycles which could be selectively pressurized by an air compressor or by a hand pump to accommodate various riding conditions. The variable resistance pneumatic spring is mounted on an existing coil spring shock body comprising a cylindrical, substantially vertical body having a threaded exterior to accept a spring preload adjuster nut, a central recess to receive a strut into the superior end and a means for attachment to the wheel assembly or bicycle frame on the inferior end; a strut with a first end slidably secured within the central recess of the body member and a second end with a means for attachment to the bicycle frame assembly or to the wheel assembly; a progression cone that slides over the body member and is held in place by the preload adjustment nut, said progression cone being substantially cylindrical with a conical upper portion; a substantially hollow cylindrical pressure casing of a greater diameter than the body member and including a latex rubber seal that extends beyond the casing's lower, open end before looping back upward and over the lip of the progression cone and culminating in a central compression seal with an interior diameter equal to the exterior diameter of the body member; a pair of retaining plates that secures the top of the outer casing to the bicycle frame assembly; and a valve assembly to regulate the intake and discharge of gas to the pressure chamber formed by the interior of the outer casing, gasket and retaining plates.
The installation of the variable resistance pneumatic spring device requires the removal of the spring retainer and the coil spring from the bicycle's existing shock absorber. The progression cone is then placed over the shock absorber body and rests on the spring preload adjustment nut. The pressure casing is then inserted over the body and the compression seal is placed around the body member in the graduated recess formed by the diagonal lineation of the mouth of the progression cone as it abducts from the body member. As the rubber gasket material progresses from the compression ring it passes over the mouth of the progression cone before looping up to bear against the interior wall of the pressure casing. The lower retaining plate is placed over the strut on the superior end of the pressure casing and the upper retaining plate is fastened to the lower retaining plate sandwiching the rubber seal and forming a hermetically sealed pressure chamber within the pressure casing. A valve mechanism is attached to the upper retaining plate with access to the pressure chamber. A pressurization source such as an air compressor or bicycle pump is used to pressurize the pressure chamber, as needed depending upon how much cushion is desired. The pressurization of the chamber forces the compression seal into the graduated recess formed between the mouth of the progression cone and the shock body to create a tighter seal as the pressure within the chamber increases. When the pressure effected upon the wheel is greater than that within the chamber, the shock body is forced into the pressure chamber thereby further compressing the air sealed within said chamber. The shock body travels into the pressure casing and the rubber gasket rolls between the progression cone and the pressure casing to form a pocket inferior to the exterior flared portion of the progression. The pocket grows progressively larger as the progression cone moves further into said casing and displaces compressed air from the chamber into the resulting lower pocket via the narrow channel between the gasket at the widest point of the progression cone and the gasket alongside the pressure casing. The displaced air is forced back into the chamber as the load on the wheel member is decreased.
2. Description of the Prior Art
There are other suspension device designed for bicycles. Typical of these is U.S. Pat. No. 5,829,773 issued to Babak Rajace on Nov. 3, 1998.
Another patent was issued to Antonio Cabrerizo-Pariente et al. on Mar. 10, 1998 as U.S. Pat. No. 5,725,226. Yet another U.S. Pat. No. 5,667,234 was issued to Wolfgang Zirk on Sept. 16, 1999 and still yet another was issued on Jun. 3, 1997 to Chin-Sung Tsai as U,S, Pat. No. 5,634,652.